Spectrophotometric Determination of Trace Thallium with Cadion 2B Using Polyurethane Foam as an Adsorption _ separating Material

It was investigated that the color reaction of thallium with Cadion 2B in the NH3-NH4Cl medium at pH 11.5～12.5 with Triton X-100. Thallium(Ⅲ) and Cadion 2B form a 1∶4(molar ratio)red complex with apparent molar absorptivity 9.3×104 L·mol-1·cm-1 at 500 nm of detection wavelength. The coloration of the reaction is completed for an instant at room temperature and the color is stable at least for 12 h. Beer's law is obeyed in the mass concentration range of 0～800 μg/L for thallium. A method for the determination of trace amount of thallium by spectrophotometry was established using polyurethane foam as an adsorption _ separating material. The proposed method is rapid and accurate and has been applied to determine trace amounts of thallium in geological samples in aqueous solution with recoveries of 97.0%～106%. The relative standard deviations(n=5) are less than 4.1%. The results obtained are in good agreement with the values obtained by AAS.